In a magnetic recording disk drive, data is written by thin film magnetic transducers called “write heads” that are supported over the surface of the disk while the disk is rotated at high speed. Each write head is located on the trailing surface of a slider that is supported by a thin cushion of air (an “air bearing”) produced by the disk's high rotational speed.
A prior art thin film inductive write head is shown in the side sectional view of FIG. 1 and the partial end view, as seen from the disk, of FIG. 2. FIG. 1 also depicts the pole tips facing a magnetic recording disk that has a magnetic layer ML on the disk substrate SB and a protective overcoat OC on the ML. The distance D from the ends of the pole tips to the middle of the ML is referred to as the magnetic spacing. The write head includes a coil C located between bottom and top pole pieces P1 and P2, respectively. The pole pieces are formed from thin films (“layers”) of magnetic material and have a pole tip height dimension commonly called the “throat height”. The throat height is measured between an air-bearing surface (“ABS”), formed by polishing the tips of the pole pieces, and a “zero throat level”, where the bottom pole piece P1 and the top pole piece P2 converge at the write gap G. A thin film inductive write head also includes a “pole tip region” which is located between the ABS and the zero throat level, and a “back region” which extends back from the zero throat level to and including a back gap BG. Each pole piece has a pole tip in the pole tip region and a back portion in the back region. The pole pieces are connected together at the back gap BG. The pole tips are extensions of the bottom and top pole pieces P1 and P2 of the write head. Each of the pole pieces P1 and P2 transitions to a pole tip (PT2 and PT1a, Pt1b) in the pole tip region. The pole tips are separated by a gap G, which is a thin layer of nonmagnetic material, typically sputter deposited insulating alumina (Al2O3) or plated nickel-phosphorous (NiP). During the write process, write currents are sent to the coil C and a magnetic field is generated across the write gap G. The fringing field from the write gap G is used to reverse the magnetization in the magnetic layer ML, resulting in the recording of data on the disk. The width W of the pole tip PT2 (FIG. 2) determines the width of the data track on the disk.
The write head shown in FIGS. 1 and 2 is depicted as part of a prior art “merged” read/write head that employs a magnetoresistive (“MR”) read element and an inductive write element in combination. The MR read element is located between bottom shield S1 and top shield S2. The bottom shield S1 is formed on a substrate, typically the trailing surface of an air-bearing slider. The top shield S2 also functions as the bottom pole P1 of the write head. In the merged MR head the pole tip of pole P1 is constructed as a narrow “pedestal” pole tip portion PT1b on top of the second shield layer S2, as shown in FIG. 2, with the P1/S2 layer then serving as a wider bottom pole tip portion PT1a. Both of these pole tip portions PT1b and PT1a form the pole tip of the bottom pole P1, with the pole tip portion PT1b forming a pedestal on the pole tip portion PT1a. In the write head shown in FIG. 1, the throat height is less than the height of PT1b because P2 does not converge at precisely where PT1b begins but at a point closer to the ABS.
The write field contour generated by the pole tips of a thin field inductive write head has a three-dimensional shape, referred to as the write “bubble”. The shape of the write bubble is defined by all points in space where the field is equal to the write threshold, which is the field strength sufficient to change the magnetization in the magnetic layer of the disk, i.e., the coercivity of the magnetic layer. For a given deep-gap field at the throat region of the write head, a larger write gap results in a wider write bubble along the in-track direction to yield better overwrite performance, i.e., the ability to overcome the influence of previously written data. However, a larger write gap also results in a wider write bubble in the off-track direction to yield a wider data track, thereby decreasing the track density that can be achieved on the disk.
To improve on this fundamental tradeoff between overwrite performance versus track density, what is needed is a thin film inductive write head that can create an improved write bubble geometry with a higher in-track to off-track aspect ratio. Such an improvement is especially desirable for very high data density applications, where overwrite performance is typically severely compromised by the need for small write gaps to maintain closely-spaced and narrow data tracks.